There are various systems for portable wireless communications equipment, for instance, GSM (Global System for Mobile Communications) and DCS1800 (Digital Cellular System 1800) widely used mostly in Europe, PCS (Personal Communications Services) used in the U.S., and PDC (Personal Digital Cellular) used in Japan. According to recent rapid expansion of cellular phones, however, a frequency band allocated to each system cannot allow all users to use their cellular phones in major cities in advanced countries, resulting in difficulty in connection and thus causing such a problem that cellular phones are disconnected during communication. Thus, proposal was made to permit users to utilize a plurality of systems, thereby increasing substantially usable frequency, and further to expand serviceable territories and to effectively use communications infrastructure of each system.
However, when the use of a plurality of systems is desired, a user has to carry a necessary number of portable communications equipments corresponding to each system, though there was conventionally no small, light-weight, portable communications equipment capable of communicating by a plurality of systems. What is necessary to enable a single portable communications equipment to use a plurality of systems is to provide the portable communications equipment with parts for each system. High-frequency circuit parts are needed for each system, for instance, a filter for passing a transmission signal of a desired transmission frequency, a high-frequency switch for switching a transmission circuit and a reception circuit and an antenna for emitting a transmission signal and receiving a reception signal in a transmission system; and a filter for passing a signal of a desired frequency among reception signals passing through the high-frequency switch in a reception system. This makes a portable communications equipment unsuitably expensive with increased volume and weight, and to achieve a portable communications equipment capable of using a plurality of systems, the portable communications equipment should have miniaturized, composite-functioning high-frequency circuit parts compatible with frequencies of a plurality of systems.
Accordingly, an object of the present invention is to provide a miniaturized, high-performance, high-frequency switch circuit capable of switching transmission circuits and reception circuits of a plurality of systems with high-frequency switches, as a high-frequency circuit part used in a portable communications equipment, which permits a single portable communications equipment to be compatible with a plurality of systems.